The present invention concerns a novel system for commanding a device implanted in a patient from an external command unit.
Microprocessor-based programmable cardiac pacemakers, which are implanted within the body of a patient, are in wide use today. These pacemakers can be communicated with from an external programmer, to alter the operating parameters of the implanted pacemaker. The pacemakers can be programmed to perform selected operations or to perform a telemetry function by returning information to the external programming device in a selected manner.
Some prior art programmable pacers are communicated with through a serial binary code format. Various transmission methods are used to transmit the binary code, such as magnetic reed switch, ultrasound, infrared signals, radio frequency pulses and bursts, amplitude modulation and frequency modulation.
The proper function of the communication link is of utmost importance to the operation of the pacer and ultimately to the well-being of the patient. There is a concern that the communication link may be affected by improper external sources, such as electromagnetic radiation emitted from various sources including therapeutic equipment. In addition, there may be improper interference from a programming code emitted by a programming device that is not intended to be used with the particular pacer that is implanted in the patient.
Certain prior art units include a read switch enabling the programming circuit to operate. The reed switch operates as a simple switch which is closed by the application of a magnetic field. The reed switch is in the implant and an external magnet closes the switch to commence the operation. One method of programming is by external magnetic pulsations which force the reed switch to open and close to provide the data signals to the implant circuitry.
In U.S. Pat. No. 4,361,153, assigned to the assignee of the present invention, a system is described in which a carrier signal from the programmer is transmitted to a tank circuit inthe implant. The tank circuit reflects back to the external programmer a wave formed with the signal data impressed thereon. The signal data is derived from a microprocessor which is coupled to sensors for various pacer functions such as rate, battery level, etc. If it is desired to change a function of the implanted pacer, the implant tank circuit acts as an antenna and receives the information. Instead of being reflected with signal data that is provided to the tank circuit, it is coupled to the microprocessor for providing the signals to the microprocessor which were received from the external programming circuit for making the desired change.
While the programming and telemetry system may be relatively complicated, it is desirable to be able to effect a simple command from an external source, to perform a selected routine. For example, if a patient simply wants to determine the battery condition of the pacer, the use of complex programming or telemetry should not be required. There are many selected routines which are relatively simple and which may be desired without the requirement of complex programming or telemetry. For example, as stated above, the patient or physician may want to take the pacer out of its sensing mode and simply check the implant battery. In another routine, the physician may simply wish to place the pacer into a temporary special pulse rate. As another possible routine, the physician may want to simply place the pacer into a temporary overdrive routine.
It is thus desirable to have the ability to provide an external command, and from this external command enable a predefined function within the implanted pacer.
It is desirable to provide a system in which a predefined function within the pacer can be enabled, without the use of a magnetic reed switch.
It is, therefore, an object of the present invention to provide a system in which a relatively simple external command device may be provided for commanding the implanted pacer to execute a selected function.
It is also an object of the present invention to provide security so that the command signal that is being transmitted from the external source to the implant is the proper command signal from the external command unit rather than some extraneous signal or rather than a signal from an improper command unit.